During the manufacture process of the glass substrate, the glass substrate is desired to take off from the high temperature cavity to the low temperature cavity. The operating processes will be completed in the closed cavity. In the prior art, the condition of entering and outing from the high temperature cavity of the glass substrate is recorded by a profession software. Using the profession software, it can be determined that whether the glass substrate is existed in the high temperature cavity or not. When the equipment is on examining or repairing, the glass substrate has been draw out from the high temperature cavity. And then, if the recording information cannot be updated in time, then the next feeding process and the exhausting process will be out of control, so that the mistaking probability in manufacture processes will be raised. Therefore, it is necessary to provide a detection device and method for detecting something existed in the high temperature cavity.